U.S. patent number 6,700,121 [Application Number 10/428,372] was granted by the patent office on 2004-03-02 for methods of sampling specimens for microanalysis.
This patent grant is currently assigned to Imago Scientific Instruments. Invention is credited to Steven L. Goodman, Thomas F. Kelly, Richard L. Martens.
United States Patent |
6,700,121 |
Kelly , et al. |
March 2, 2004 |
Methods of sampling specimens for microanalysis
Abstract
Methods of sampling specimens for microanalysis, particularly
microanalysis by atom probe microscopy, include steps of forming a
study specimen in a first study object (as by use of focused ion
beam milling); removing the study specimen from the study object;
situating the study specimen on a second study object; and
microanalyzing the study specimen. Where the first study object is
of particular interest for study, the study specimen may be taken
from a functional portion of the first study object so that
microanalysis will provide information regarding this functional
portion. Where the second study object is of particular interest
for study, the second study object may be subjected to
manufacturing processes (e.g., deposition of layers of materials)
after the study specimen is situated thereon so that the study
specimen will provide information regarding the results of the
manufacturing process. The study specimen may have study regions
formed thereon which are particularly suitable for study by atom
probes, e.g., regions bearing raised protrusions, at virtually any
point during the process, thereby greatly enhancing the speed and
efficiency of specimen preparation.
Inventors: |
Kelly; Thomas F. (Madison,
WI), Martens; Richard L. (Madison, WI), Goodman; Steven
L. (Madison, WI) |
Assignee: |
Imago Scientific Instruments
(Madison, WI)
|
Family
ID: |
22762259 |
Appl.
No.: |
10/428,372 |
Filed: |
May 1, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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861405 |
May 18, 2001 |
6576900 |
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Current U.S.
Class: |
850/52; 216/2;
250/304; 438/14; 850/33; 850/34; 850/35 |
Current CPC
Class: |
G01N
1/32 (20130101); Y10T 436/25 (20150115) |
Current International
Class: |
B81C
1/00 (20060101); B81B 1/00 (20060101); G01N
1/32 (20060101); G01N 001/32 () |
Field of
Search: |
;250/307,304 ;216/2
;438/14 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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197 55 990 |
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Mar 1999 |
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DE |
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0 784 211 |
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Jul 1997 |
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EP |
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7-43373 |
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Feb 1995 |
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JP |
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2001208659 |
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Aug 2001 |
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JP |
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Other References
Nishikawa, O. and Kimoto, M., Toward a scanning atom probe-computer
simulation of electric field, Appl. Surf. Sci. 76/77:424-430
(1994). .
Nishikawa, O., Kimoto, M., and Ishikawa, Y., Development of a
scanning atom probe, J. Vac. Sci. Technol. B, 13:599-602 (1995).
.
Nishikawa, O., Ohtani, Y., Meada, K., Watanabe, M., and Tanaka, K.,
"Development of the Scanning Atom Probe and Atomic Level Analysis,"
Materials Characterization, vol. 44 (2000) pp. 29-58. .
Kelly, T.F., Camus, P.P., Larson, D.J., Holzman, L.M. and Bajikar,
S.S., On the many advantages of local electrode atom probes,
Ultramicroscopy 62:29-42 (1996). .
Kelly, T.F. and Larson, D.J., "Local Electrode Atom Probes,"
(Invited review) Materials Characterization, vol. 44 (2000) pp.
59-85. .
Giannuzzi, L.A., "A Tutorial of the FIB Lift-out Technique for TEM
Specimen Preparation," Microac. Microanal. 5 (Suppl. 2:
Proceedings), Springer Verlag (1999) pp. 516-517. .
Sheng, T.T., Goh, G.P., Tung, C.H., and Wang, L.F., "Precision
transmission electron microscopy sample preparation using a focused
ion beam by extraction method," Journal of Vacuum Technology B,
May/Jun. 1997. .
International Search Report for PCT/US01/16185..
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Primary Examiner: Berman; Jack
Attorney, Agent or Firm: Fieschko, Esq.; Craig A. DeWitt
Ross & Stevens S.C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation claiming priority under 35 USC
.sctn.120 to U.S. patent application Ser. No. 09/861,405 filed May
18, 2001, now U.S. Pat. No. 6,576,900 which in turn claims the
benefit under 35 USC .sctn.119(e) of U.S. Provisional Patent
Application No. 60/205,456 filed May 19, 2000. The entireties of
these applications are incorporated by reference herein.
Claims
What is claimed is:
1. A method of preparing a specimen for atom probe microanalysis
comprising: a. forming one or more regions on an object, the
regions being suitable for atom probe microanalysis; b. subjecting
one or more of the regions to a manufacturing process wherein zones
of different materials are defined on the regions; and c.
thereafter microanalyzing at least one of the processed regions
with an atom probe.
2. The method of claim 1 wherein the manufacturing process is a
layer deposition process.
3. The method of claim 1 wherein the manufacturing process is
chosen from at least one of spin casting, photolithography,
epitaxial thin film deposition, and ion implantation.
4. The method of claim 1 wherein the regions are separated from the
object prior to the step of microanalysis.
5. The method of claim 4 wherein the separated regions are situated
on or within a second object prior to the step of
microanalysis.
6. The method of claim 1 wherein the regions are separated from the
object after the step of defining zones of different materials on
the regions.
7. The method of claim 1 wherein the step of forming regions on the
object includes forming one or more protrusions on each region.
8. The method of claim 7 wherein the protrusions are formed by
removing material from the object about the boundaries of each
protrusion.
9. The method of claim 1 wherein the object is a semiconductor
wafer.
10. The method of claim 1 wherein the object contains an integrated
circuit.
11. The method of claim 10 wherein at least one of the regions is
situated adjacent to the integrated circuit.
12. A method of preparing a specimen for atom probe microanalysis
comprising: a. defining a region suitable for atom probe
microanalysis on an object; b. depositing material on the region;
and c. thereafter microanalyzing the region with an atom probe.
13. The method of claim 12 wherein the step of defining the region
includes forming a protrusion on the object.
14. The method of claim 13 wherein the step of forming the
protrusion on the object includes removing material from the object
to leave the protrusion remaining.
15. The method of claim 12 wherein the object is a semiconductor
wafer.
16. The method of claim 12 wherein the object contains an
integrated circuit.
17. The method of claim 16 wherein at least one of the regions is
situated adjacent to the integrated circuit.
18. The method of claim 12 wherein the region is separated from the
object prior to material deposition.
19. The method of claim 12 wherein the region is separated from the
object prior to microanalysis.
20. The method of claim 19 wherein the region is separated from the
object after material deposition.
21. The method of claim 19 wherein: a. the separated region is
placed on or within a second object, and b. material is then
deposited onto the second object and separated region together.
22. The method of claim 19 wherein: a. the separated region is
placed on or within a second object, and b. the second object and
the separated region are then microanalyzed together.
23. A method of preparing a specimen for atom probe microanalysis
comprising: a. defining one or more regions on an object, each
region containing one or more protrusions suitable for atom probe
microanalysis; b. depositing material on at least one of the
regions; and c. thereafter microanalyzing at least one of the
regions with an atom probe.
Description
FIELD OF THE INVENTION
This disclosure concerns an invention relating generally to methods
for obtaining and preparing specimens for microscopic analysis, and
more specifically to methods of obtaining and preparing specimens
for micron-scale and sub-micron-scale analysis, particularly
specimens of multilayered materials, and materials upon which thin
films have been deposited, implanted or otherwise incorporated
(e.g., semiconductor wafers, photonic devices).
BACKGROUND OF THE INVENTION
In the manufacture of many modern devices containing
microscopically thin layers of different materials, and/or zones of
different materials segregated on a microscopic scale, it is
important to be able to study the different layers and/or zones
with analytical equipment after the deposition. As examples, it is
often useful to be able to microscopically analyze the structures
of semiconductor microelectronic devices; magnetic thin film memory
storage devices (such as read/write hard disk heads and platters);
thin film based optical devices; multilayered polymeric, organic
and/or biochemical based thin film devices (as used in medicine);
composites of inorganic materials, organic materials and/or
biological materials (such as bioMEMs, biosensors, bioarray chips,
and integrated labs on chips); and other devices wherein nanoscale
structures are critical to device function. Common equipment used
for such analysis (hereinafter referred to as "microanalysis")
includes electron microscopes (including TEMs, Transmission
Electron Microscopes, and SEMs, Scanning Electron Microscopes);
spectrometers (including Raman spectrometers and Auger
spectrometers); photoelectron spectrometry (XPS); Secondary Ion
Mass Spectrometry (SIMS); and more recently, the atom probe
microscope, as described in U.S. Pat. Nos. 5,061,850 and 5,440,124.
Of course, other microanalysis equipment is available, and new
equipment having different principles of operation is expected to
become available over time.
Generally, microanalysis of an entire device is not feasible owing
to practical constraints, and thus specimens of portions of the
device are studied. Ideally, the specimen of the device under study
is formed from the actual material that is intended to perform a
function in the device. Accordingly, destructive testing methods
are known wherein study specimens are "biopsied" from the objects
being studied, and are then subjected to microanalysis. As an
example, Focused Ion Beam (FIB) milling processes are often used to
excise study specimens from study objects. A good background
discussion of FIB processes is set forth in U.S. Pat. No. 6,042,736
to Chung. U.S. Pat. No. 6,188,072 is then of interest for its
discussion of a method (allegedly described by the FEI Company of
Hillsboro, Oreg. USA) of cutting a study specimen from a study
object by FIB milling, with the study specimen then being removed
by a micromanipulator by use of electrostatic attraction. The study
specimen is then subjected to TEM microanalysis. The remainder of
the patent is directed to a micromanipulator suitable for
performing this operation. U.S. Pat. No. 6,188,068 to Shaapur et
al. appears to describe a similar method, and the Background
section of U.S. Pat. No. 5,270,552 also appears to describe similar
methods for preparing study specimens using FIB milling and
mechanical cutting/polishing steps.
U.S. Pat. No. 6,194,720 to Li et al. describes a method wherein a
study object is milled by FIB and other processes to produce a thin
cross-sectional study specimen suitable for microanalysis by a TEM.
One aspect of the method involves milling a pair of parallel
trenches in the top surface of the study object to define a
plate-like first study region therebetween (FIGS. 2A-2C of Li et
al.), and then filling in the trenches with filler material (FIG.
2D). Portions of the study object are then cut away along planes
parallel to the first study region and intersecting the filled
trenches (FIG. 3B), or being spaced a short distance away from the
filled trenches (FIG. 3C). As a result, the study object is formed
into a plate-like shape wherein the first study region defines an
area of decreased thickness. The plate-like study object is then
milled into a wedge-like form (FIGS. 4A and 4B) wherein the thinner
side(s) of the study object define a second study region. The first
and second study regions thereby define thin plate-like areas on
the study object wherein the various deposited layers of the study
object are displayed. A somewhat similar arrangement is described
in U.S. Pat. No. 5,656,811, which is more directly devoted to
methods of controlling the FIB milling process.
U.S. Pat. No. 5,270,552 describes a process wherein a study
specimen is partially severed from a study object using FIB milling
(with the study specimen remaining attached to the study object by
a thin bridge of material), a probe is then connected to the
partially-disconnected study specimen (as by "soldering" it thereon
with FIB deposition), and then the study specimen is fully removed
by cutting away the bridge with FIB milling so that the probe may
carry the study specimen to a desired location for study. By using
an electrically conductive probe, the voltage between the probe,
study specimen, and bridge can provide a measure of whether the
study specimen is intact. The probe may also serve as a support
structure for further preparation of the study specimen, or for use
during the study specimen's microanalysis. Use of the process to
obtain multiple study specimens from points spaced about a
semiconductor wafer is illustrated. The patent additionally
discusses the use of the underlying process steps to separate
elements from one chip, transport them to another chip by use of
the probe, and then sever the probe and "solder" the elements to
the second chip by use of FIB deposition.
Other patents note that study specimens can be formed from a study
object by use of material removal processes other than FIB
processes (and any accompanying polishing or other mechanical
material removal processes). U.S. Pat. No. 6,140,652 to Shlepr et
al. describes the formation of study specimens from a study object
for TEM microanalysis using photolithography and chemical etching
processes. Trenches are etched in the study object to form a
circular plug-like study specimen, which then has its base cut free
from the study object by further chemical etching techniques. The
study specimen can then be microanalyzed using TEM techniques.
In many instances, destructive testing (as in the foregoing
methods) is undesirable because it will effectively render the
study object inoperable. Thus, in some cases "proxy" or "qualifier"
study objects are used: objects which are not the true study
objects of interest, but which are subjected to the same processes
so that they (hopefully) serve as a reasonable representation of
the product generated by these processes. As an example, in the
field of semiconductors, many thin film deposition systems are
designed to deposit layers over an area greater than the size of a
typical semiconductor wafer. Qualifier wafers are often processed
alongside actual wafers so that they receive the same deposited
layers as the production wafer. The qualifier wafer is then
destructively tested in place of the actual wafer. However, testing
of a qualifier wafer assumes that the qualifier wafer receives the
same treatment as the actual wafer within the deposition system, an
assumption which is not always valid because the deposited coatings
may vary in time or location within the deposition system.
One significant problem encountered with all known methods is the
time and expense of subsequent testing. Often, individual study
specimens, once obtained in accordance with the foregoing methods,
must then be individually prepared for subsequent microanalysis.
This can include steps such as polishing, mounting, application of
protective or other layers, situating the study specimen in a
vacuum environment, and so on. Because of the disadvantages of
destructive test methods, and because of the time and expense
involved in the microanalysis of individual study specimens, there
is a need for new methods of microanalysis which are nondestructive
(or at least minimally destructive), and which are better suited
for rapid processing of multiple study specimens.
SUMMARY OF THE INVENTION
The invention involves methods which are intended to at least
partially solve the aforementioned problems. To give the reader a
basic understanding of some of the advantageous features of the
invention, following is a brief summary of preferred versions of
the methods. As this is merely a summary, it should be understood
that more details regarding the preferred versions may be found in
the Detailed Description set forth elsewhere in this document. The
claims set forth at the end of this document then define the
various versions of the invention in which exclusive rights are
secured.
The invention includes methods of obtaining and preparing
specimens, particularly specimens of thin film materials and other
materials having distinct zones of different materials arrayed on a
micron or sub-micron scale (e.g., integrated circuit wafers), for
study by microanalysis equipment. The invention is particularly
suitable for preparing specimens for microanalysis with an atom
probe, which is a preferred mode of microanalysis because it can
produce three-dimensional compositional images with atomic-scale
resolution. This capability of atom probes is especially attractive
for studying and characterizing the small-scale structures
typically found in microelectronic devices that are used, for
example, in integrated electronic circuits and the read/write heads
of data storage devices. Historically, atom probes have utilized a
needle-shaped study specimen (or a study specimen having a
needle-shaped study region formed thereon), since such a needle
shape is beneficial for creating the high electric fields required
for atom probe microanalysis. Where the study specimen or study
region is wire-shaped, this shape readily lends itself to needle
creation; otherwise, the region to be studied must be cut into a
suitable needle-like shape, as by FIB milling. Planar structures
like wafer-processed materials, e.g., microelectronic materials,
are often difficult to cut into atom probe specimens because the
structures of interest exist only in a very thin layer on the
surface of the specimen that is often less than about 10
micrometers (microns) thick. However, with advances in atom probe
technology, and with the advent of scanning atom probes and local
electrode atom probes, it is possible to use atom probes to
microanalyze specimens that are raised in relation to their
surroundings by as little as a few micrometers, and which are
closely spaced (e.g., by no more than a few micrometers away) in
relation to adjacent protrusions. For example, local electron atom
probes only require a small protrusion on the specimen (a few
microns high) for the local electrode to be able to locally apply
the necessary extraction field to the specimen in order to effect
ionization.
In a first preferred version of the invention, a study specimen is
formed from a larger first study object such as an integrated
circuit wafer, as by cutting the study specimen therefrom by the
use of FIB milling. The study specimen will generally be a portion
of the first study object item which is of key interest for
microanalysis, e.g., a functional section of a semiconductor chip.
The study specimen is then removed from the first study object, and
is situated on a second study object such as a silicon-based wafer
whereupon the study specimen is microanalyzed. Preferably, the
study specimen (and perhaps several other study specimens) are also
inserted within recesses in the second study object, and/or are
affixed to the second study object (as by FIB deposition). The
study specimen(s) can then be microanalyzed on the second study
object, which can be constructed and configured to enhance the
speed and ease of microanalysis; for example, the second study
object may be formed of a material which promotes electrostatic
attraction of the study specimen to the second study object (either
by itself or with the assistance of an applied charge), thereby
assisting in the placement of the study specimen on the second
study object.
In a second preferred version of the invention, a study specimen is
formed from a larger first study object such as a silicon-based
wafer, as by cutting the study specimen therefrom by use of FIB
milling. The study specimen is removed from the first study object
and is situated on a second study object, with the second study
object in this case generally being the item of primary interest
for microanalysis rather than the first study object. The study
specimen (and perhaps multiple other study specimens) can
additionally be inserted within recesses formed in the second study
object, and/or can be affixed to the second study object (as by FIB
deposition). Where the study specimen is recessed within the second
study object, it is often also useful to render the study specimen
at least substantially coplanar with the second study specimen, as
by the use of polishing processes. The second study object (with
the study specimen thereon) is then subjected to any desired
manufacturing processes, e.g., layer deposition processes, so that
the study specimen and second study object both reflect the results
of such processes. The study specimen may then be microanalyzed for
desired information regarding the effects of the manufacturing
process, preferably after removal from the second study object.
Here, the second study object (and more specifically the effect of
the manufacturing process on the second study object) is of primary
interest for microanalysis, but the study specimen is analyzed in
place of the second study object so that the second study object
may be left intact, without the need to excise a portion of the
second study object (as is done to the first study object in the
first version of the invention). During the foregoing process, the
study specimen is preferably placed on a nonfunctional portion of
the second study object so that the study specimen does not
interfere with the effects of the manufacturing process on the
second study object; for example, where the second study object is
a semiconductor chip bearing an integrated circuit, the study
specimen is preferably placed on a portion of the chip which does
not bear the circuit so that the circuit emerges from the
manufacturing process in an operable state.
Where an atom probe is used for microanalysis of the study
specimens, it will generally be useful to form study regions on the
study specimens wherein protrusions are defined for generation of
the desired extraction voltage. The study regions (and the
protrusions therein) may be formed in the study specimens at the
outset of the foregoing methods (e.g., when the study specimens are
first formed), or near the end of the foregoing methods (e.g.,
immediately prior to microanalysis). Formation of the study regions
during construction of the study specimens themselves is
particularly preferred for sake of speed and efficiency, and
methods are described later in this document for allowing such
early formation of the study regions without leading to significant
degradation in the quality of data obtained during later
microanalysis.
The invention is particularly well adapted to allow sampling of
objects for microanalysis while the objects are being manufactured,
with minimal or no damage to the object being sampled, and with
exceptionally rapid preparation of specimens for microanalysis.
Further advantages, features, and objects of the invention will be
apparent from the following detailed description of the invention
in conjunction with the associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top perspective view of a study specimen 102 formed in
a first study object 104 prior to its removal therefrom (with a
micromanipulator 110 suitable for such removal being shown in
phantom).
FIG. 2 is a top perspective view of a second study object 202 which
serves as a specimen holder wherein a study specimen similar to
that of FIG. 1 is placed during microanalysis, with an enlarged
view of the second study object 202 being shown wherein numerous
study specimens 208 are inserted.
FIG. 3 is a top plan view of several study specimens 302 formed
from a first study object 304 (or a portion thereof), with the
study specimens being suitable for removal and later
microanalysis.
FIG. 4 is a top perspective view of a second study object 404 which
is to be subjected to layer deposition or other manufacturing
processes, and which has study specimens 402 similar to those of
FIG. 3 placed thereon prior to such processes so that the study
specimens 402 can later be removed to study the effects of such
processes.
FIG. 5 is a top perspective view of a study specimen 502 similar to
those of FIGS. 3 and 4, wherein four study regions 504 suitable for
microanalysis in an atom probe have been defined.
FIG. 6 is a top perspective view of a second study object 602
similar to that of FIG. 4, but wherein study specimens 606 are
placed both on and within the second study object 602.
FIGS. 7 and 8 illustrate a side elevational view of a manipulator
714 useful for placing study specimens 702 within a second study
object 706 (as illustrated in FIG. 6) and removing them
therefrom.
FIG. 9 illustrates, in views (a)-(e), exemplary steps for
processing a study specimen 902 having a predefined study region
906 having protrusions 908 suitable for microanalysis by an atom
probe.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
In a first version of the invention, a study specimen is formed
from a larger study object, such as a semiconductor wafer of
interest, using methodologies similar to those previously described
for TEM specimen preparation. The study specimen is then situated
on a second study object which effectively serves as a specimen
holder. The study specimen is microanalyzed while resting on the
specimen holder, preferably by an atom probe after the study
specimen has had study regions formed thereon (e.g., raised study
regions) which are well-suited for atom probe microanalysis. A more
detailed description follows.
Initially, a study specimen is formed in a larger study object of
interest, such as a semiconductor wafer. Once the area of interest
on the study object is identified as the area from which the study
specimen is to be obtained, a study specimen can be formed in the
study object at this area using known cutting techniques such as
FIB milling, etching, and so forth. An example is illustrated in
FIG. 1, wherein a study specimen 102 is formed in a surface 104 of
a study object by using FIB milling to form two adjacent parallel
trenches 106 in the study object surface 104; joining the trenches
106 at their ends so that the study specimen 102 is defined by a
freestanding cantilevered wall; and then milling away a portion of
the base of the wall so that the study specimen 102 is connected to
the study object 104 by a small tether 108.
The study specimen 102 may then be broken from the study object 104
at its tether 108, and the study specimen 102 may be removed from
the study object 104 by use of a micromanipulator (such as the ones
described in U.S. Pat. No. 6,188,072 and elsewhere). A pincers-like
micromanipulator having opposable jaws 110 is illustrated in FIG.
1, and by grasping the study specimen between the jaws 110 while
tilting the study specimen 102 into another plane, the tether 108
may be broken so that the study specimen 102 can be easily
removed.
The study specimen 102 is then placed on a second study object
which serves as a specimen holder during later microanalysis. Most
preferably, the second study object includes a number of recesses
whereby the study specimen 102 may be placed in a desired recess,
and additional study specimens may be placed in other recesses, so
that the second study object may be situated in an atom probe
apparatus or other microanalyzer so that some or all of the various
study specimens 102 may be sequentially or simultaneously
microanalyzed. FIG. 2 illustrates an exemplary second study object
202 having a central storage area 204 wherein several recesses 206
are formed, with each site being marked, or the sites being
logically arrayed, so that study specimens 208 placed within the
recesses 206 may be more easily correlated with their recesses 206
(thereby allowing for easier later identification of the placed
study specimens 208). The recesses 206, as well as any associated
markings, may be formed in the second study object 202 by various
processes such as FIB milling, deep etching, and/or electroforming.
The recesses 206 preferably extend through only a part of the
thickness of the second study object 202 rather than through its
entire thickness. It should be understood that any storage area 204
wherein study specimens 208 are stored need not be situated in a
central location on the second study object 202, nor need it have
boundaries which are complementary to the boundaries of the second
study object 202, as shown in FIG. 2; rather, the recesses 206 may
be arrayed to define storage areas 204 of any size or shape, or
multiple storage areas 204 which each contain a discrete set of
recesses 206 can be defined and arranged as desired on a second
study object 202. Where the second study object 202 is a standard
6-inch diameter silicon wafer, approximately 1600 recesses 206 can
be formed in the second study object 202 wherein study specimens
208 having dimensions of approximately 20 micrometers long and 2
micrometers wide may be stored. FIG. 2 illustrates study specimens
208 having these dimensions which have been processed to each bear
three study regions 210 suitable for microanalysis by an atom
probe, as by milling away adjacent areas of the study specimens 208
so that the study regions 210 remain as rod-like raised
protrusions. Such milling could occur after the study specimens 208
are received within their respective recesses 206, or it could
instead be performed beforehand, e.g., during the initial formation
of each study specimen 208 from its first study object.
The second study object 202 is preferably made of a material which
promotes electrostatic attraction between a study specimen 208 and
the second study object 202, and/or which may be charged to
selectively attract or repel the study specimen 208 as desired. As
an example, where a study specimen 208 is extracted from a
semiconductor wafer, the second study object 202 may be constructed
from a silicon wafer or from copper. Thus, if desired, a voltage
may be applied to the second study object 202 so that the study
specimen 208 is electrostatically attracted to the surface of the
second study object 202 and to a recess 206 therein. If the
recesses 206 extend through the entire thickness of the second
study object 202 so as to effectively define passages therein, it
is also possible to situate material beneath the second study
object 202 which is well-suited for generation and/or storage of an
electrostatic charge, whereas the second study object 202 might not
itself be well-suited for such generation and/or storage. In this
case, the electrostatic attraction to the study specimen 208 can be
effectively isolated to the recesses 206.
After the study specimens 208 are placed in or on the second study
object 202, the second study object 202 can be readied for use in
an atom probe by affixing the study specimens 208 to the second
study object 202, as by using FIB deposition of a metal, or by
applying an adhesive or solder, at the boundaries where the study
specimens 208 abut the second study object 202 (or by affixing the
study specimens 208 to the second study object 202 at areas which
are preferably located away from the study regions 210, e.g., by
affixing the regions situated between the study regions 210 to the
second study object 202 at the areas labeled 212). Where
microanalysis is to be performed by other than an atom probe, other
types of final preparation prior to microanalysis can be performed
(e.g., deposition of protective layers, polishing, etc.). The
second study object 202, and any study specimens 208 provided
thereon or therein, may then be placed in an atom probe or other
microanalyzer so that selected study specimens 208 may be
microanalyzed.
In this first preferred version of the invention, study specimens
are taken from a first study object of interest (wherein the first
study object has usually already been subjected to processing,
e.g., to layer deposition methods), and the study specimens are
placed on a second study object for microanalysis (with the second
study object perhaps being chosen to have desired material
properties which enhance the speed and ease of microanalysis, but
wherein the second study object is usually not of direct interest
for study). A second preferred version of the invention follows
similar steps, but in a sense can be said to represent a situation
where the first and second study objects exchange roles. In this
second version, the study specimens are taken from a first study
object which may be chosen to have desired material properties (but
wherein the first study object is usually not of direct interest
for study itself), and the study specimens are placed on a second
study object which is subjected to layer deposition or other
manufacturing processes. The study specimen (and more particularly
its deposited layers) is then microanalyzed, preferably by an atom
probe after the study specimen has had regions formed thereon
(e.g., raised study regions) which are well-suited for atom probe
microanalysis. The study specimens may then be microanalyzed on the
second study object, or more preferably after removal from the
second study object. In effect, the study specimens serve as proxy
or qualifier specimens which are associated with and subjected to
the same processes as the second study object, and can therefore be
studied in lieu of the second study object to serve as its proxy
and avoid destructive testing of the second study object (though
the study specimens may themselves be destructively tested). A more
detailed description follows.
Initially, one or more study specimens are formed in a first study
object. This can be done by milling or otherwise forming the study
specimens from the first study object in the manner previously
described with reference to FIG. 1, but it is also possible to form
study specimens from the first study object in bulk. This scheme is
illustrated in FIG. 3, wherein an exemplary set of study specimens
302 is shown affixed within a specimen matrix 304 formed from a
first study object, such as a thin silicon wafer or other material
which is etched or otherwise processed to generate the specimen
matrix 304. Regarding silicon study specimens 302, suitable wafer
"blanks" for creation of the specimen matrix 304 are available from
Virginia Semiconductor, Fredericksburg, Va. (USA). The study
specimens 302, which include protruding handles 306, are connected
by thin tethers 308 to the framework 310 of the specimen matrix
304. Thus, when a handle 306 or other portion of a study specimen
302 is sped by a micromanipulator (such as the one illustrated in
phantom in FIG. 1), its study specimen 302 may be tipped out of the
plane of the matrix framework 310 to break its tethers 308 and
allow the study specimen 302 to be removed. By repeating a specimen
matrix pattern such as the one shown in FIG. 3, an arbitrarily
sized wafer can be made to include a very large number of study
specimens 302.
Referring then to FIG. 4, after a study specimen 302 is removed
from the first study object (and from its specimen matrix 304, if
present), it may be situated by the micromanipulator on a second
study object as depicted at 404. The second study object 404 is in
this version of the invention the study object of key interest, and
is illustrated as a silicon wafer which has not yet undergone some
or all of its processing steps (e.g., all material layers have not
yet been deposited). FIG. 4 illustrates five study specimens 402
situated on the second study object 404, with the intent being that
the study specimens 402 will accompany the second study object
through some or all of its subsequent processing steps so that they
receive the same treatment as the second study object 404. Thus,
when the study specimens 402 are subsequently microanalyzed, they
should reveal information regarding the processing of the second
study object 404 without requiring that the second study object 404
be destructively tested. It should be understood that the study
specimens 302 shown on the second study object 402 are not shown to
scale, and they would generally be much smaller with respect to the
second study object 402. Additionally, it should be understood that
more or fewer than five study specimens 302 can be placed on the
second study object 402, though the five-point placement of FIG. 4
will often be sufficient because it allows testing of parameters
along two directions with three test points in each direction.
Also, since it will generally be desirable to have the second study
object 404 emerge from processing as a complete and operable
article of manufacture, it should be understood that the study
specimens 402 are preferably situated on the second study object
404 in nonfunctional blank or "dead" locations on the second study
object 404 so that their presence does not interfere with
processing of the second study object 404 in critical functional
locations.
It will often be useful to choose materials for the study specimens
402 such that they have generally the same adhesion and other
characteristics as the second study object 404 when layers are
deposited, and/or the second study object 404 is subjected to other
manufacturing processes, so that the study specimens 402 will
accurately represent the second study object 404 after processing.
For example, when the second study object 404 is a semiconductor
chip which is primarily composed of silicon, a silicon study
specimen 402 is recommended for use to provide a proxy which will
demonstrate substantially the same level of layer adhesion as the
second study object 404. It is also useful to choose materials for
the study specimens 402 such that they demonstrate some degree of
adhesion to the second study object 404 via electrostatic
attraction, and/or so that they can be made to exhibit such
adhesion when a charge is applied to the second study object 404.
Taking again the example of a second study object 404 which is
primarily composed of silicon, a silicon study specimen 402 is
recommended because it will directly and strongly adhere to the
second study object 404, and such study specimens 402 can be can be
made to stick or release to the second study object 404 by applied
voltage. The ability to promote adhesion and removal of the study
specimens 402 by the second study object 404 and/or by
micromanipulators facilitates automation of the process. The
affixment mechanism between the study specimens 402 and the second
study object 404 could be by means other than (or means additional
to) electrostatic attraction, for example, by magnetic forces,
application of solders or polymeric adhesives, or other forms of
attachment. However, it is desirable that any mode of affixment
used be easily reversible in order to facilitate the removal of the
study specimens 402, and any adhesive (if one is used) should not
significantly interfere with the treatment of the study specimens
402 during the manufacturing process (i.e., the study specimens 402
should accurately receive and reflect the effects of the
manufacturing process).
After the second study object 404 has undergone some or all
processing steps, one or more selected study specimens 402 can be
microanalyzed by one of the aforementioned microanalysis tools (or
others), either while resting on the second study object 404 or
after being removed therefrom. Removal can occur by use of the
aforementioned micromanipulators, and where atom probe
microanalysis is to occur, study regions (e.g., raised "hills" or
rods) may be formed on the removed study specimen(s) 402 prior to
microanalysis. FIG. 5 illustrates a study specimen 502 wherein four
study regions 504 suitable for atom probe microanalysis have been
formed by FIB milling or other etching methods. It should be
understood that more or fewer study regions may be formed on a
study specimen as desired, and as dictated by the size of the study
specimen and the level of detail achievable by the etching method
being used.
In a third preferred version of the invention not explicitly shown
in the accompanying drawings, the placement of multiple study
specimens 402 on the second study object 404 is simplified by
taking a specimen matrix bearing multiple study specimens 402, such
as the specimen matrix 304 of FIG. 3, and placing the entire
specimen matrix on the second study object. The framework of the
matrix (i.e., the part of the matrix apart from the study
specimens) may then be adhered to the second study object so that
any one or more study specimens 402 are easily removable from the
framework and the second study object by breaking them off at the
tethers connecting them to the framework. The second study object
may then undergo processing, and any of the desired study specimens
402 may be microanalyzed on the second study object or after being
removed therefrom.
A fourth preferred version of the invention (illustrated in FIG. 6)
follows most of the steps of the second version discussed above,
but here the second study object 602 is formed with (or has formed
therein) recesses 604 which have shapes complementary to those of
the study specimens 606. The recesses 604 are preferably formed by
etching, milling, or other processes at nonfunctional blank or
"dead" locations on the second study object 602 so that they do not
interfere with the functionality of the second study object 602.
The recesses 604 preferably have a depth such that the study
specimens 606, when inserted therein, rest flush with (or very
close to flush with) the surface(s) of the second study object 602
whereupon the recesses 604 are formed. After insertion of study
specimens 606 within the recesses 604 (and after affixing the study
specimens 606 therein, if desired), surface polishing may be used
so that the exposed surface(s) of the study specimens 606 are
effectively coplanar with the exposed surface(s) of the second
study object 602. Thus, when the study specimens 606 rest upon and
within the second study object 602, they are more likely to obtain
the same treatment as the second study object 602 during layer
deposition processes since they will rest in at least substantially
the same plane. This version of the invention accounts for the
possibility in the second version of the invention that the study
specimens may receive different treatment because their surfaces
that receive deposited layers may rest in a different plane than
the surfaces of the second study object that receive deposited
layers. This version of the invention is therefore useful where the
processing methods to which the second study object 602 is
subjected require uniform deposition of fluids, e.g., spin casting
and certain photolithographic processes, and wherein study
specimens 606 which present a top surface which is not coplanar
with the second study object 602 might not accurately represent the
treatment of the second study object 602 during processing. For
other fabrication processes such as epitaxial thin film deposition
and ion implantation, study specimens 606 which are several microns
thick, and which are not coplanar with the second study object 602
(as in the second version of the invention), should reflect little
or no appreciable difference in processing treatment and should
therefore present a generally accurate depiction of the second
study object 602.
An arrangement which can be used to speed placement of the study
specimens in the fourth version of the invention is illustrated in
FIGS. 7 and 8. Here, a study specimen 702 similar to the study
specimens 606 is shown inserted within a recess 704 formed in a
second study object 706. The first study object (not shown) from
which the study specimen 702 is formed has a magnetically
susceptible layer 708 provided thereon so that the study specimen
702 may be more easily manipulated with the application of magnetic
force. Such a layer 708, if not provided on the first study object,
can be deposited on a surface of the first study object using
standard deposition processes. Rather than placing the study
specimen 702 within the recess 704 of the second study object 706
with a friction fit, the study specimen 702 is affixed therein by a
bonding agent 710 which allows reversible bonding and removal by
application of heat (e.g., an alloy such as indalloy or a low
melting temperature polymeric adhesive). An automated robotic
device 712 having a manipulator 714 and a movable arm 716 is also
shown wherein the manipulator 714 has an electromagnet therein, and
also preferably some form of an emitter capable of activating the
bonding agent 710. To remove the study specimen 702 from the second
study object 706 for analysis, the manipulator 714 is moved above
the study specimen 702 within the second study object 706, and the
magnetically susceptible layer 708 may be used to precisely
position the location of the manipulator 714 via a force feedback
mechanism from its electromagnet. To remove the study specimen 702,
the manipulator 714 applies an appropriate activation energy to
cause the study specimen 702 to be loosened from the recess 704,
whereupon the electromagnet of the manipulator 714 then withdraws
the study specimen 702 and holds it to the manipulator 714 for
transport. Depending upon how the study specimen 702 is bonded
within its recess 704, the manipulator 714 could apply heat (as by
infrared illumination) to melt a solder or polymer, apply
ultraviolet light to degrade a polymer or other adhesive, or apply
another form of activation energy to the bonding agent 710. If the
study specimen 702 is frictionally fit within the recess 704,
applied magnetic force from the manipulator 714 may be sufficient
in itself to remove the study specimen 702. Preferably, the face of
the manipulator 714 which meets the study specimen 702 has a recess
718 formed therein in order to help prevent damage to the processed
surface of the study specimen 702. The arm 716 is then retracted to
pull the study specimen 702 away from the second study object 706,
and can be used to transport the study specimen 702 for subsequent
microanalysis.
As previously noted, where study specimens are to be analyzed by
use of an atom probe (the preferred form of microanalyzer for use
with the invention), it is useful to form raised study regions in
the study specimens prior to microanalysis. While such study
regions are often formed by FIB milling processes, they can also be
fabricated by a number of photolithographic and surface roughening
methods known in the art. Such study regions may be formed prior
to, during, or after the various steps described above; for
example, the study regions may be formed in the study specimens
prior to their removal from the first study object, or may instead
be formed immediately prior to microanalysis. It was previously
noted that where certain types of layer deposition processes are
used (such as spin casting), it is helpful to have the exposed
surfaces of the study specimen rest flush with the exposed surfaces
of the second study object so that discontinuities in the exposed
surfaces will not alter the morphology of the deposited layers. In
similar fashion, where these "sensitive" layer deposition processes
are used, it may be less useful to form study regions in the study
specimens prior to layer deposition since the discontinuous
surfaces of the study regions might also affect the layer
morphology. If a study specimen bearing pre-formed study regions is
subjected to a layer deposition process which is sensitive to the
discontinuous surfaces surrounding the study regions, the study
specimen will still be usable for microanalysis since the central
axes of any protrusions in the study regions will be minimally
affected by layer deposition irregularities. However, any adjacent
sloping or significantly depressed areas of the study regions may
have such significantly different morphology that they will not
accurately represent the layers deposited on the second study
object, and therefore preformed study regions, while allowing
easier processing of study specimens, may result in a study
specimen yielding less useful information. A method is therefore
illustrated in FIG. 9 wherein any preformed study regions in a
study specimen may effectively be hidden during deposition
processes so that such study regions will not distort the results
of such processes during later microanalysis.
Referring to FIG. 9 at (a), a study specimen 902 (with magnetically
susceptible layer 904) is shown with a top study region 906
including several preformed protrusions 908 suitable for analysis
in an atom probe. It is desirable to subject the study region 906
to a manufacturing process, e.g., a layer deposition process,
wherein the protrusions 908 will accurately reflect the results of
the layer deposition process. As noted above, if a sensitive
deposition process is used, the protrusions 908 may only provide an
accurate representation of the process near their central axes
unless steps are taken to remedy the effects that the spaces 910
between the protrusions 908 have on the sensitive deposition
process.
In FIG. 9 at (b), the spaces 910 between the protrusions 908 are
filled in with a filler material 912 to provide a uniform planar
top surface on the study specimen 902. The filler material 912 is a
sacrificial layer which will be removed after the study specimen
902 is subjected to the layer deposition process, and it may be
formed of polymers, solders, evaporated metals, or other materials.
The filler material 912 may itself include multiple layers. For
example, the base layer of the filler material 912 could be formed
of a material which does not strongly adhere to the study specimen
902, and subsequent layers may then be chosen to facilitate the
removal of the entirety of the sacrificial filler material 912; for
example, evaporated nickel could allow later magnetic removal of
the filler material 912. Alternatively, certain polymers or alloys
could be chosen for combination as filler material 912, and for
ready removal by a combination of irradiation or heating combined
with suction, or by application of ultrasonic energy.
In FIG. 9 at (c), the study specimen 902 is subjected to a layer
deposition process, resulting in layer 914 resting atop the study
specimen 902 and filler material 912.
In FIG. 9 at (d), the filler material 912 is destroyed and/or
removed along with corresponding portions of the deposited layer
914; for example, the removal mechanism 916 might be a suction
device which serves to pull filler material 912 having low bonding
strength from the study specimen 902, or a magnetic device which
serves to pull magnetic filler material 912 from the study specimen
902. Since the deposited layer(s) 914 resting atop the filler
material 912 are very thin and adhere to the filler material 912 to
a greater extent than they adhere to surrounding portions of the
deposited layer(s) 914, they will be removed along with their
underlying filler material 912.
It is understood that the various preferred embodiments are shown
and described above to illustrate different possible features of
the invention and the varying ways in which these features may be
combined. For example, it was described above which aspects of the
first and second preferred versions of the invention were
interchangeable, and which aspects of the second and third
preferred versions of the invention were interchangeable. It should
therefore be apparent in accordance with the teachings set forth
herein that other aspects of the various versions of the invention
are also interchangeable. To illustrate, the study specimens 102 in
the first version of the invention (and as shown in FIG. 1) could
be configured similarly to the study specimens 302 in the second
version of the invention (and as shown in FIG. 3), and the specimen
holder/second study object 202 of FIG. 2 could be configured
similarly to the second study object 602 of FIG. 6. Thus, referring
to FIG. 6, the first version of the invention would utilize study
specimens 606 received and microanalyzed within the second study
object 602. As another illustration, the robot 712 of FIG. 1 could
be used in conjunction with the study specimens 208 of FIG. 2. In
similar fashion, numerous other combinations are regarded as being
within the scope of the invention.
Apart from combining the different features of the above
embodiments in varying ways, other modifications are also
considered to be within the scope of the invention. Following is an
exemplary list of such modifications.
First, if desired, prior to milling, etching, or otherwise forming
study specimens, recesses in study objects, etc., the operator may
apply a protective layer to the study object and/or the area of the
study specimen, as discussed by U.S. Pat. Nos. 6,140,652,
6,188,068, 6,194,720, and others.
Second, apart from the pincer-like micromanipulator 110 illustrated
in phantom in FIG. 1 and the electrostatic and magnetic
micromanipulators previously mentioned, numerous other types of
micromanipulators can be used in the practice of the invention. For
example, attraction and repulsion of study specimens could also
occur by gas pressure (i.e., the application of vacuum and/or
pressurized gas). It is noted that while micromanipulators such as
the micromanipulator 110 are often actuated by piezoelectric
elements, direct manipulation by piezoelectric elements, as by
inserting a piezoelectric element into an aperture in a study
specimen and expanding and contracting the element to grasp and
release it, is also possible.
Third, other means of affixing the study specimens to the second
study object apart from electrostatic attraction, magnetic
attraction, chemical and/or mechanical adhesion, friction fitting,
etc. are possible. Another example of a useful reversible form of
affixment is to form a protrusion on a portion of a study specimen,
and form a receiving recess within the second study object, whereby
a mechanical (and more then merely frictional) fit between the
specimen and object is achieved. For example, a study specimen may
bear a protrusion having an irregular cross-section defined about
an axis of rotation, and a study object may have a recess which may
receive the protrusion in lock-and-key fashion, such that insertion
of the protrusion within the recess and rotation therein will
prevent withdrawal of the protrusion along its axis of
rotation.
Fourth, while it was previously noted that the second study object
may be marked for easier identification of study specimens situated
thereon (as with the markings shown adjacent the recesses 206 in
FIG. 2), it is also possible to provide such markings on a study
specimen itself. It is noted that markings need not be alphanumeric
characters, and could instead be bar codes or other
encoded/patterned markings, fluorescent markers, and/or any other
features allowing unique identification of study specimens and/or
their locations on study objects.
Fifth, while the portions of the foregoing discussion dealing with
the definition of study regions focused on study regions having
protrusions well-suited for atom probe analysis, it is noted that
study regions suitable for microanalysis by one or more other forms
of microanalyzers are also feasible. As an example, apart from
raised protrusions, study regions might instead (or additionally)
bear elongated slabs or other shapes useful for TEM analysis. Study
regions having shaped surfaces useful for analysis by several
different types of microanalyzers are also possible, e.g., a
protrusion-bearing slab or wedge formed for both atom probe and TEM
analysis.
Sixth, while most of the foregoing examples assumed that inorganic
materials such as silicon would be used for study specimens and/or
study objects, the invention may accommodate use of organic
materials as well. Biological and organic materials may require
special processing to maintain structure during specimen
preparation due to the lability of such materials. For example,
some materials may be in a frozen hydrated state at all stages of
preparation in vacuum, for example, during FIB treatment and atom
probe microanalysis. Alternatively, biological and organic
materials may require chemical fixation, dehydration, and drying by
means known in the art to prepare them for scanning electron
microscopy. Since organic and dried biological materials have very
low electrical conductivity, this may require coating the specimen
with carbon or evaporated metals prior to FIB etching to create the
proper geometry for imaging.
Preferred embodiments of the invention have been described above in
order to illustrate how to make and use the invention. The
invention is not intended to be limited to these embodiments, but
rather is intended to be limited only by the claims set out below.
Thus, the invention encompasses all alternate embodiments that fall
literally or equivalently within the scope of these claims.
* * * * *